Preparation of sols



Patented Dec. 30, 1947 [UNITED STATES PATENT. "OFFICE 2,433,778 I Morrisfil i nfto flw iifassignor to Monsanto Chemical Company, St. Louis, Mo.,

a, corporation of Delaware V No Drawing. Original application September3,

, 1941, Serial No.

409,434, now Patent No.'

2,386,247, dated October 9, 1945. Divided and this application August28, 1945, Serial No.

1 Claim. (01. 252-309) This invention relates to the p reparation 'osols, and particularly to the preparation of substantially anhydrous andsalt free organosols, such as sols containing certain'alcohols, ethers,ether-alcohols, esters, ketones, hydrocarbons and the like as thecontinuous'phase.

There are severalknownpmethods formaklng substantiallyanhydrousorganosols. For example, it is old to add alcohol to aqueoussilicic acid, and then to remove the water by such means as dialysis or.exposure in a confined space to the drying action of dry carbonate'ofpotash or quicklime. It is also old to add glycerine to a 2% colloidalsilicic acid solution with heat and agitation, and then to evaporate thewater to obtain a clear transparent, highly viscous mass of colloidalsilicic acid in glycerine. However, the products prepared in the abovemanner are either of low concentration or of :low stability andtherefore are not suitable for many'indu'strial purposes for which theymight otherwise be adapted.

It is accordingly a primaryobject of this invention to prepare verystable and highly dispersed inorganic oxide sols in substantiallyanhydrous organic solvents which are of unusually high concentrations,e. ;g;containas much as twenty-five percent oxide ormore.

A further object of the invention is to prepare sols of the typedescribed containing either watermiscible or Water-immiscibleorganicsolvents as the continuous phase.

A further object of theinvention is to prepare substantially anhydroussols of a relatively high degree of concentration and stabilitycontaining either aromatic or aliphatic hydrocarbons as the continuousphase.

A still further object of the invention is to prepare sols of the abovenature which contain only a relatively small amount of inorganic salt.

Still further objects and advantages of the invention will appear fromthe following description and appended claim. Before explaining indetail the present invention, however, it is to be understood that theinvention is not limited in its application to, the details describedherein, since the invention is capable of other embodiments and of beingpracticed or carriedvout in various ways. Also it is to beunderstoodthat the phraseology orterminology employed herein is for thepurpose of description and not of limil 2 tation, and it is not intendedto limit the invention claimed herein beyond the requirements of theprior art.

The invention is in general carried out by first forming an aquasolcontaining a colloidal inorganic oxide and a dissolved inorganic salt,then adding a water-miscible organic solvent to the aquasol in an amountsufiicient to precipitate the inorganic salt and to permit substantiallycomplete removal of the water by distillation, thereafter removing theprecipitated inorganic salt, as by tfiltration, centrifuging or thelike, and iinally removing the water by distillation.

The above process results in the production of organosols which aresubstantially free of water, i. e. contain not more than about 1% ofwater. Products containing only traces of water may, however, easily beobtained in accordance with the invention by subjecting the above solsto a second or third distillation, which may or may not involvereplacement of the original organic solvent with another organicsolvent. Although the organic solvent initially employed should bemiscible with water, the solvent used to replace it may be eitherwater-miscible or water-immiscible.

The organic solvent initially employed should be of such a nature as tocause substantially complete precipitation of inorganic salts and shouldeither have a boiling point higher than that of water, i. e.suiiiciently higher to permit substantially complete removal of thewater by simple distillation, or it should be capable of forming aconstant boiling mixture with water, either by itself or in combinationwith a thirdor a plurality of additional components, which mixture can Ithen be fractionally or otherwise distilled oil",

leaving as the residue 2. sol containing the de-- sired organic liquidas the dispersing medium or continuous phase. A most suitable solventfor forming a binary C. B. M. (constant boiling mixture) with water isnormal propyl alcohol, which not only is highly miscible with water, butis relatively cheap and may be readily obtained in large quantities.Ethyl alcohol may also be used in accordance with this invention, but asethyl alcohol does not form a satisfactory binary C. B. M. with waterfor the purposes of this invention, a third component, such as benzene,dichloroethylene, trichloroethylene, and the like, is added,

ily processed, as by replacement, to produce sols having relatively loWboiling or high boiling water-miscible or immiscible organic solventsas;

the continuous phase. For example, the ethyl or propyl alcohol in thesols D ieParedas-described. above may be replaced with such organicliquids as Cellosolves, high boiling alcohols, ethers, ether- Iprecipitaltethe saltat temperatures of not above alcohols, ketones,esters, aliphatic and aromatic hydrocarbons and the like, by mixing-theinitial alcohol sol with one or more of the above solvents anddistilling off the initial alcohol", either as such or in the form of aconstant boiling mixture.

The resulting sols have been found toicontain even less water than thesols prepared directly from theconstant boiling. mixtures.

As. suitable organic. solvents or liquids for replacing the initialalcohol sols may bementioned such substances as Cellosolve, methyl and.butyl Cellosolve, the butyl and amyl alcohols, diethyl Cellosolve,diethyl Carbiton, methyl isobutyl ketone,. ethyl and butyl acetate,benzene, toluene, and aliphatic hydrocarbons, such as lactol spirits.

Another method of further reducing the water content .of sols formedfrombinary constant boiling mixtures,such asthepropyl alcohol sol preparedas described above, involves forming a ternary constant boiling mixturebyadding to the resulting sol an. organic solvent, such asbenzene,.dichloroethylene, and trichloroethylene and an. additionalquantity of the original organic'solvent, and then. fractionally.distilling the resulting ternary. mixture. 'I-hedistillation product isan .organosol containing only a trace of water. Thus, in thecase ofpropyl alcohol it is possible to distill off both .binaryand ternaryconstant boiling mixtures with theresult lthat sols having this alcoholas thecontinuousphasemaybe readily made containing very minute amountsof water.

The sols prepared from ternary constant boil.- ingmixturesand-containing only a trace of water, such as-thepropyl alcohol and likesols prepared as described immediately above, may 'bereadlly convertedto sols containing. water.- immiscible organic solvents as .thecontinuous phase. For example, the propyl alcohol in .such sols may bereplaced by toluenev or other hydrocarbons bymerely mixing. thehydrocarbon with the substantially water .free alcoholsolanddistillin'gtheresulting mixture. Sols of this nature are ordinarily'verydiflicultto obtain, but may be readily prepared in accordance withthe above method.

The organic solvent orliquid. employed should be added to theaquasol insuflicient amounts not only to precipitate the. inorganic salt containedtherein, but to prevent .gelation. during the early stages .of the.distillation. during which-water is removed. an=d.to permitsubstantially complete removal of-thewater. This usually results in theformation of an intermediate.organo-aquasol containing about 3% silica.

, Theaquasols treated or used in connection-with theeaboveprocessesmaybe prepared in various In the case of silica sol, forexample, they ways.

are preferably prepared by reacting an aqueous solution of sodiumsilicate with dilute sulfuric acid in suitable proportions. Any othersuitable method may however, be employed, depending upon the particularoxide sol which it is desired to prepare.

In general, it is preferable to use aquasols having a high concentrationof the colloidal oxide in connection with the. processes-of thisinvention, as this permits the" use of less organic solvent than wouldotherwise be required to precipitate out the inorganic salt and alsorequires less distillation to remove water.

It is also usually preferable, particularly in the case. of silicasols,-to prepare the aquasol and to l5 C. Moreover, it is usuallypreferable to prepare and use-'anaquasol having a pH of between j 2 and4' to insure' maximum stability during the -20.

preparation of the :organosols. However, the invention should. not..belimited in these respects, as it is possible to obtain stable andsubstantially anhydrous: sols of high concentration without resorting totemperaturesbelow normal, and without operating in the above mentionedpH range.

A more complete. and. thoroughmnderstandin of the invention will be.obtained from the. following. examples:

Example I .Three hundred. fifty.- eight .pounds of sodiumsilicatecontaining 28.7% SiOz, 8.9%

NazO and 62.4% Hzoare dilutedwith onehundredsixty-two 'poundsof water.This mixture is then added. toone lhundred sixty-three and one-halfpounds-of 3l% sulfuric. acid and the mass is agitatedto distribute thesilicate throughout the acid. Themixingis carried out in a suitableacidresistant-apparatus at a temperature of about 15 C., and results.ina silica-sol having a pH of about 2.5; One thousand :three hundred andseventy-fivepounds of .Cellosolve are then addedto-the soL-graduallywith. stirring, 1 while maintaining the temperature at about 15 C. Thiscauses precipitationof the inorganic salt, which is then removedbyifiltering.orcentrifuging; To the. cleanse one. thousand five hundredand fortypounds of additional ..Cellosolve are added. so thatihe SiO;.contentis re.-. duced. to about 3%... The'solis thendistilled in .aleadstill equipped-with a stirrer anda. fraction.- ating column, the.distillation. being..d,iscontinued when the sol in.thestillissubstantially free of water and. contains .about25 SiO-2.-,.

Example .;II .H'Ihree hundredfiftyeeight pounds of sodiumsilicate.containing 28.7% SiO'z,i-8.9-.%. NazO and 62.4% H2O are diluted.withonehundred sixty-two. pounds of water-.1 This l .mixture is thenadded to one...hundred=sixty-three-and one-half poundsof 31% sulfuricacidand-the mass is agitated to .distribute the silicate. throughout theacid. The mixing is carried out in a suit? able acid: resistantapparatus at .atemperature of about 15C., andresults in .a- SiliC& .S.O1having a pH of about 2.5,. .-.One,thousandthree hundred and seventy-fivepounds of normal propyl alcohol are then added. to thasolgradually withstirring while. maintainingthe temperature at about 15. C. .This causes.precipitationof substantially all of the inorganic salt; .which.is then.removedby filtering or centrifuging. .I'o theclearesolone thousand fivehundred .andforty poundsof additional. normal. propyl-alcoholar added,which reducestheSiOz contentto about 3% The sol is then distilled in..alead still. equipped with a stirrer and a. fractionating column..Duringthe distillation the refluxing ratio is maintained in such amanner as to obtain 73% propanol in the first 50% of the distillate,about 92% propanol in the next 20% of the distillate, and about 99'%propancl-in the last 30%, whichleaves .as a res idue 'asolcontainingabout 25% 'SiOa.

Example -'III. Three hundred fifty-eight pounds ofsodiumsilicatecontaining 28.7% 'S'iOz, 8.9% NazO and 62.4% H2O are*dilutedwith one hundred sixty-two pounds of water. This mixture is thenadded to one hundred sixty-three and one-half pounds of 31% sulfuricacid and the mass is agitated to distribute the silicate throughout theacid. The mixing is carried out in a suitable acid resistant apparatusat a temperature of about 15 C., and results in a silica 501 having a pHof about 2.5. One thousand three hundred and seventy-five pounds ofethyl alcohol (containing about 92% CzHsOH by weight) are then added tothe sol gradually with stirring, While maintaining the temperature atabout 15 C. This causes precipitation of substantially all of theinorganic salt, which is removed by filtering or centrifuging. To theclear sol one thousand five hundred and forty pounds of additionalalcohol are added, which reduces the S102 content to about 3%. The solis then distilled in a lead still equipped with a stirrer and afractionating column having 28 theoretical plates. Eight hundred and tenpounds of benzol are gradually introduced into the top of the columnduring the first part of the run. The column is operated at capacity andthe temperature at the top is maintained at 65 C. by proper refluxcontrol, until all of the lower aqueous layer has been separated andremoved. A high reflux ratio is then maintained until all thebenzol-alcohol fraction has been removed. Substantially anhydrousalcohol is then removed at a rapid rate until the sol in the stillcontains an SlOz content of about 25%.

Ewample IV.-A mixture containing one part by weight of the 25% propylalcohol sol prepared in accordance with Example II, two parts by Weightof anhydrous normal propanol and one and one-quarter parts by weight ofbenzol is distilled in a distillation apparatus equipped with a stirrerand a fractionating column having 28 theoretical plates, which resultsfirst in the removal of the water layer which forms and then in theremoval of the C. B. M. containing normal propanol and benzol. Thedistillation is continued until the final dehydrated sol, containingonly a trace of water, has been concentrated to a 25% SiOz content.

Example V.Five parts by weight of toluene are added to one part byweight of the normal propanol sol containing 25% SiOz obtained inaccordance with Example IV. The resulting mixture is then distilled in adistillation apparatus provided with a stirrer and a fractionatingcolumn until all the normal propyl alcohol is removed as a C. B. M. andthe resulting toluene sol contains an SiOz content of about 15%.

Example VI.-Two and one-half parts by weight of butyl acetate are addedto one part by weight of the normal propyl alcohol sol containing 25%8102 obtained in accordance with Example II. The mixture is thendistilled in a distillation apparatus provided with a stirrer and afractionating column until all the normal propyl alcohol is removed,whereupon the distillation is continued until the resulting butylacetate sol residue contains about 25% Si02.

As indicated by the above examples, the method of this invention notonly permits the production of highly concentrated and stable organosolswhich are :substantially free of water, but they render .it possible to,prepare substantially salt free sols having -fa wide'variety "offorganic solvents as the continuous phase, without resorting tocumbersome 'andtinre consuming methods of removing the salt, such asdialysis or the like. The organic solvents used or present in the finalsol may be either Water-miscible or Water-immiscible, high boiling orlow boiling. Moreover, they may comprise or consist of such hydrocarbonsor mixtures of hydrocarbons, as benzene, toluene, lactol spirits or thelike, which heretofore it has not been possible to successfully prepareas sols of the type described.

Although the above examples refer solely to the preparation oforganosols containing an individual organic solvent, it should beunderstood that the invention is not limited to such sols, and that solsmay also be prepared containing mixtures of organic solvents. Forexample, an organosol may be prepared directly, using a mixture ofwater-miscible solvents instead of just one, or the solvent or solventsin the initial organosol may be replaced by any suitable mixture oforganic solvents, which in such case may be either water-miscible orwater-immiscible.

The term organic solvents employed herein and in the appended claim isintended to refer to the type of solvents commonly employed in the fieldof coating compositions, such as varnishes, lacquers, and the like, andcommonly understood by chemists as suitable for such purposes. The termis also intended to include, however, alcohols, which are usually notemployed as solvents in the coating art.

The term Cellosolve represents the mono ethyl ether of ethylene glycol,while methyl, ethyl, butyl and diethyl Cellosolve represents the methyl,ethyl, butyl and diethyl ethers of ethylene glycol respectively. Theterm lactol spirits represents a product consisting of homogeneousclosely fractionated portions of petroleum crude oil which are derivedfrom petroleum by distillation and constitute a mixture of hydrocarbonshaving an evaporation rate similar to or close to that of toluene. Theproduct has a specific gravity of .7313 at 60 F. and the following A. S.T. M. distillation range:

This application is a division of my co-pending application Serial No.409,434, filed September 3, 1941, now Patent No. 2,386,247, grantedOctober 9, 1945, which is a continuation-in-part of application SerialNo. 272,404, filed May 8, 1939, and granted June 9, 1942, as Patent No.2,285,449.

What I claim is:

The method of preparing a stable and substantially anhydrous organosolcomposed of colloidal silica and ethyl acetate which comprises formingan aquasol containing colloidal silica and a dissolved inorganic salt,adding ethyl alcohol to said aquasol in an amount sufiicient toprecipitate the inorganic salt, removing the precipitated inorganicsalt, adding additional ethyl alcohol and adding benzene in amountssufficient to permit substantially complete removal by distillation ofthe water, the alcohol being added in an amount sufficient to permitsubstantially com 7 8 v ple'te remov al of the benzene'by distillation,re- 1 UNITED STATES PATENTS-- 7 moving entirely the water and thebenzene by .v r 7 distillation, and then adding ethyl'acetate and NumberI 7 :Name. v e Date removing the ethyl alcohol by distillation.2,375,733 White y 1 v M R 5 2,386,247 Marshall Oct. 9, 1945 2,383,653.Kirk Aug. 28, 1945 REFERENQJES CITED 2,377,840 Healy June 5, 19452,391,253 Marshall -2 Dec. 18, 1945 The following references are ofrecord in the file of this patent:

